1. Field of the Invention
The present invention relates generally to pipettors. More particularly, the present invention relates to micro-pipettors used with a pipette tip.
2. Related Art
Pipettors are used to transfer fluid, preferably precise quantities of fluid. Pipettors are typically used for adding precise quantities of reagents, samples, or other types of fluids to test tubes, micro-titer wells, microscope slides, and the like. A micro-pipettor is used to dispense quantities of fluid in the micro-liter (.mu.l) range. The micro-pipettor is generally used with a pipette tip. The pipette tip typically has a very fine bore at one end through which fluid is drawn or pulled into, and expelled from, the pipette tip. The micro-pipettor to which the pipette tip is mated provides suction so that fluid is drawn into the pipette tip. The micro-pipettor can also exert a pressure in the pipette tip to expel the fluid from the pipette tip.
Conventional pipettors are configured with elongated, tubular bodies. To perform pipetting operations with such a conventional pipettor, a user's hand and arm must be in an elevated position, typically twelve to eighteen inches above the working level of the slides, test tubes, or other receptacles being used. Working with the hand and arm at the elevated position results in fatigue faster than working with the hand and arm at a position closer to the working level of the receptacles. Working at the elevated position for an extended period of time can even lead to pain and injury for the user. Further, working at the elevated position makes the fragile pointed tip of the pipettor more difficult to control, and can result in inaccurate pipetting or even piercing a gel into which the pipetting may be done. Having the user's hand and arm closer to the working level would provide better movement feedback to the user, thereby resulting in better control and a more accurate pipetting operation.
One type of conventional pipettor is a squeeze-bulb pipettor that is equipped with a squeeze bulb to draw fluid into and expel fluid from the pipettor. With such a squeeze bulb pipettor, the user holds the pipettor with one hand, and squeezes the bulb with the other to draw and expel liquid. Such two-handed operation is cumbersome, and does not allow the user a free hand to perform such tasks as aligning the pipettor, moving the reagent bottles, moving the slides or receptacle trays, etc.
Other conventional pipettors are configured for one hand operation. Such conventional pipettors typically include a movable piston or plunger to draw fluid into and expel fluid out of the pipette tip. The tubular body of the pipettor is grasped by encircling some or all of the four fingers of the hand around the pipettor. The piston is moved by longitudinal (up and down) movement of the thumb. In some conventional pipettors, longitudinal movement of the thumb is used to draw fluid into the pipette tip, and a trigger mechanism operable by one of the fingers is provided to expel the fluid from the pipette tip. These conventional pipettors require repeated up and down movement of the thumb, typically when the hand and arm are in an elevated position. Repetitive movement of the thumb in this manner over extended periods of time is not only uncomfortable, but can lead to pain and stress injuries. An alternative to thumb-operated pipettors is disclosed in U.S. Pat. No. 5,445,797. This patent discloses an elongated tubular pipettor that is held in a user's hand like a pen. In this position, the user's index finger is used to depress and release pressure on a flexible member to draw fluid into, and expel fluid from, the pipette tip.
Conventional pipettors use a variety of techniques to dispense a precise or calibrated quantity of fluid. For example, U.S. Pat. No. 5,125,278 discloses a volumetric squeeze-bulb type pipette having two branches. A liquid sample is drawn up into one branch by squeezing a bulb, and a precise volume is expelled by squeezing a bulb on the second branch. Other pipettors are calibrated so that a linear movement of the piston is related to a volume change within the pipettor. A precision mechanical control mechanism is used to move the piston, and to relate the distance moved to the volume of liquid either pulled in or pushed out of the pipettor.
Micro-pipettors can use a graduated pipette tip to dispense a calibrated quantity of fluid. Such a graduated pipette tip includes graduation marks that are calibrated to measure precise quantities of fluid drawn into the pipette tip. The pipette tips are made from a transparent or translucent material to allow the user to visually compare the level of fluid drawn into the pipette tip with the graduation marks. In other micro-pipettors, linear movement of a piston or plunger is related to change in volume. In such micro-pipettors, a precision mechanical control mechanism is used to move the piston, and to relate the distance moved to the volume of liquid either pulled in or pushed out of the micro-pipettor. The pen pipettor disclosed in U.S. Pat. No. 5,445,797 provides for a coarse draw calibration by limiting the draw of the pipettor. However, it has been found in practice that although such a coarse draw calibration provides a reproducible quantity of fluid, it does not provide an accurate quantity of fluid. Therefore, such a coarse draw calibration cannot be relied upon to provide an accurate quantity of fluid.
Conventional pipettors do not take advantage of the natural opposable movement between the thumb, and fingers and palm of a user's hand. Thus, there is a need in the art for an ergonomically designed pipettor that allows all pipetting operations to be performed with one hand, and that accurately dispenses a calibrated quantity of fluid. Conventional pipettors also do not provide a way to easily perform multiple simultaneous pipetting operations. Thus, there is a further need in the art for a pipetting apparatus that can be easily configured to perform multiple simultaneous pipetting operations.